1. Field of the Invention
This invention relates to a low temperature starting system for internal combustion engines running on middle distillate fuels and other low volatility alternative fuels, including single and multi-cylinder compression ignition, spark ignition, and surface ignition engine configurations.
The invention is applicable to internal combustion engines operating on a wide variety of liquid and gaseous fuels in vehicle applications, stationary applications, and portable applications such as generator sets. The invention allows for extremely low temperature starting of an engine with minimal expenditure of cranking energy, minimal cranking duration and speed, and minimal time between initiating the starting system and sustained engine operation.
Internal combustion engines operate by combustion processes which take place in the cylinders (combustion chambers of the engine). In spark ignition engines a combustible air/fuel mixture is drawn into the combustion chamber where a spark or ignition source is used to ignite the mixture causing expansion of the combustion gases, thereby producing power at the crankshaft. The air/fuel mixture must be inducted at a temperature sufficient to promote partial vaporization of the fuel. If the temperature of the mixture is too low, vaporization of the fuel will not be sufficient to produce a combustible mixture at the ignition source during the compression stroke, and the engine will not start.
The minimum ambient temperature at which unaided starting can occur depends on the type of fuel used. Low volatility fuels such as JP5, JP8, and diesel fuels will not allow spark ignition engine starting even at room temperature without low temperature starting aids.
In compression ignition engines air is drawn into the combustion chamber where it is compressed. Compression causes the temperature of the air to increase. When the fuel is injected into the combustion chamber, it mixes with the hot air and spontaneously combusts if a sufficient quantity of air-fuel mixture in the combustion chamber is above the auto-ignition temperature of the fuel. Auto-ignition causes the combustion gases to expand and power is produced at the crankshaft. The auto-ignition temperature of conventional compression ignition fuels is typically quite high, for example diesel fuel has an auto-ignition temperature range between 700.degree.-900.degree. F. The maximum combustion chamber temperature prior to sustained combustion is dependent on the compression ratio of the engine. If the mixture temperature in the combustion chamber does not reach the auto-ignition temperature, the injected (atomized) fuel will not ignite and the engine will not start. Auto-ignition is discussed in detail in Internal Combustion Engines and Air Pollution by Edward F Obert (Intext Educational Publishers).
At low ambient temperatures, the air-fuel mixture in the combustion chamber does not reach the auto-ignition temperature upon compression due to the low temperature of the inducted air and the high rate of heat loss to the engine components during compression. If the rate of heat build-up in the combustion chamber does not exceed the rate of heat transfer out of the combustion chamber, the engine will not start.
2. Description of the Prior Art
Ancillary fuels, such as ether, have been used as an aid in starting internal combustion engines at low ambient temperatures. U.S. Pat. No. 4,938,180 employs a controlled ether injection system to allow low temperature starting. The high volatility and rapid preparation rate of ether during the compression stroke creates a combustible mixture at low temperatures which aids in starting spark ignition engines. The low auto-ignition temperature of the air/ether mixture aids in starting compression ignition engines.
However, there are many drawbacks to using ether as a starting aid. Its low auto-ignition temperature causes premature combustion and undesirably high rates of combustion pressure rise (knock) in compression ignition engines, and may also cause overspeeding of the engine upon startup since compression ignition engines usually do not have any means of controlling the rate at which the air/ether mixture is inducted.
The high volatility, anesthetic properties, and low auto-ignition temperature of ether also present a safety hazard with regard to storage and use. In addition, ether tends to dry the cylinder walls of the engine resulting in excessive engine wear.
Numerous other methods have been employed to improve low temperature starting capabilities. Many of these have involved preheating major engine components such as the engine block, cylinder head, etc. These methods require very large expenditures of energy due to the large mass of metal that is heated. Some compression ignition engines have electrically powered glowplugs in pre-combustion chambers, which permits the retention of a bulk temperature sufficient to ignite the injected fuel at low ambient temperatures. Glowplugs are not normally used in open chamber compression ignition engines since the area of the exhaust valves must be reduced below the optimal size to allow space for the glowplug. Substantial electrical power is required to operate a glowplug and the minimum ambient temperature at which the engine will start depends on the engine design. A further drawback is that as the temperature decreases the cranking time increases. Engine cranking, especially at low temperatures causes excessive engine wear since the engine components do not receive optimal lubrication at such low cranking speeds. Fuel ends up on the cylinder walls diluting resident lubricating oil, which dilutes the oil in the crankcase.
Other starting methods involve preheating the inducted air or air/fuel mixture to improve starting. U.S. Pat. No. 4,682,576 assigned to Mazda Motor Corporation, Hiroshima, Japan employs electric heating elements placed in the induction system of a compression ignition engine to heat the air in conjunction with a valve system which causes high intake velocities during cranking to create compressed air in the cylinder through-inertia. Electric heating elements in the inducted air stream typically require substantial energy input for a moderate increase in air temperature at cranking speeds.
In some instances, a flame source has been installed into the induction system whereby some inducted air is heated and some inducted air is used to support flame combustion. This method is limited in that increasing the inducted air temperature requires increasing the combustion heat supplied by the flame and in so doing the oxygen content of the air is depleted, impeding the tendency for combustion of the fuel in the combustion chamber.
An object of the invention is to allow compression ignition engines and low volatility fueled spark ignition engines to start at extremely low ambient temperatures with minimal cranking time (reduced engine wear) and minimal energy expenditure without using ancillary fuels. It is assumed that at low temperatures the fuels would have appropriate pour and cloud points.
Another object is to reduce exhaust emissions and white smoke during the start-up and warm-up periods at low ambient temperatures by improving the combustion processes during the start-up and warm-up period.